MATLAB Programming Fundamentals - MathWorks

Regular Expressions

In this section...

“What Is a Regular Expression?” on page 2-41

“Steps for Building Expressions” on page 2-43

“Operators and Characters” on page 2-46

What Is a Regular Expression?

A regular expression is a sequence of characters that defines a certain pattern. You

normally use a regular expression to search text for a group of words that matches the

pattern, for example, while parsing program input or while processing a block of text.

The character vector 'Joh?n\w*' is an example of a regular expression. It defines a

pattern that starts with the letters Jo, is optionally followed by the letter h (indicated by

'h?'), is then followed by the letter n, and ends with any number of word characters,

that is, characters that are alphabetic, numeric, or underscore (indicated by '\w*'). This

pattern matches any of the following:

Jon, John, Jonathan, Johnny

Regular expressions provide a unique way to search a volume of text for a particular

subset of characters within that text. Instead of looking for an exact character match as

you would do with a function like strfind, regular expressions give you the ability to

look for a particular pattern of characters.

For example, several ways of expressing a metric rate of speed are:

km/h

km/hr

km/hour

kilometers/hour

kilometers per hour

You could locate any of the above terms in your text by issuing five separate search

commands:

strfind(text, 'km/h');

strfind(text, 'km/hour');

% etc.

Regular Expressions